Low chamfer angled torque tube end fitting metal

ABSTRACT

A method of forming a torque tube ( 64 ) is provided. The method includes forming a fitting ( 80 ) having an elongated tube conforming area ( 88 ). The conforming area ( 88 ) includes chamfer areas ( 82 ) having upper surfaces ( 90 ), lower surfaces ( 92 ), and chamfer surfaces ( 94 ) that transition between the upper surfaces ( 90 ) and the lower surfaces ( 92 ) and have chamfer angles ( 96 ) of approximately 20 relative to the lower surfaces ( 92 ). An elongated tube ( 86 ) is procured and an end portion ( 106 ) of the elongated tube ( 86 ) is formed onto the conforming area ( 88 ) to form a torque-transmitting coupling ( 84 ). The torque tube ( 64 ) is also provided and formed according to the above-stated method.

TECHNICAL FIELD

[0001] The present invention relates generally to vehicle systems, and more particularly, to a torque tube and a method of manufacturing the torque tube.

BACKGROUND OF THE INVENTION

[0002] Torque tubes are typically used for mechanically transmitting torque from power drive unit to a rotating device that provides translation motion. For example, a torque tube is commonly used in a ground-based vehicle to transfer torque from an engine to a front or rear axle, which in turn rotated wheels of the vehicle providing propulsion. Another example is in an aircraft whereby a torque tube may be utilized for transmitting torque between a power drive unit and a ballscrew, which is providing either horizontal or vertical translation of airfoil surface adjusting devices such as flaps and slats.

[0003] Many applications of torque tubes, including the above mentioned, require that the torque tube be lightweight, inexpensive, have high fatigue strength, and an ultimate yield strength at an end fitting equal to or exceeding that of the tube itself. Thus, torque tubes for aircraft are formed from 2024 aluminum due to its inherent lightweight and strength characteristics over that of steel.

[0004] A typical torque tube has an elongated tube section, which is conformed over a fitting. The fitting has multiple chamfered surfaces between a pair of upper flat surfaces and multiple lower flat surfaces with chamfer angles that are approximately 45 relative to the lower surfaces. The upper surfaces transition to the chamfer surfaces at relatively sharp chamfer edges. The fitting also has multiple overflow groves that transition between recessed areas and the lower flat surfaces, via groove edges.

[0005] The chamfer edges and the groove edges cause notches to be formed in the elongated tube, when being conformed over the fitting. Thinning occurs in the elongated tube near the notches and can cause fatigue cracking over time. Cracking, as known in the art, reduces fatigue life of a component and is therefore undesirable.

[0006] Elongated tubes are normally procured having a T-3 temper condition. The elongated tubes are treated with a chemical film such as alodine to create a corrosive inhibiting surface coating. The elongated tubes are heat treated for an extended period of time in a furnace such that the elongated tubes are of a solid solution or in a W tempered condition. A disadvantage with heat treating the elongated tubes is that the corrosive inhibiting surface coating is negatively affected during the heat treatment. The elongated tubes are placed in a freezer, to maintain the W condition and prevent aging of the tubes, up until electromagnetic forming over the end fittings.

[0007] During forming of the elongated tubes, tube walls are significantly thinned. Due to stretching and thinning of the tube walls, the tubes are weakened and are susceptible to cracking under fatigue. Thinning can be difficult to detect by ordinary inspection procedures without destructive testing.

[0008] Upon completion of forming the elongated tubes, depending upon length of the tubes, the tubes are hand straightened. The elongated tubes are then naturally aged to a T-42 temper until a significant amount of tubes are ready for artificial aging, due to costs of operating a furnace as to perform artificial aging. The elongated tubes are artificially aged in a furnace to again alter temper of the tubes from having a T-42 temper to having a T-62 temper, which is of strength suitable for application use.

[0009] The above-mentioned process of manufacturing a torque tube is time consuming and costly due the amount of steps within the process and the requirements for each step.

[0010] It is therefore, desirable to provide a method of manufacturing a torque tube that provides a more durable chamfer portions with increased fatigue life, minimizes warping of the elongated tubes, and has decreased production cycle times and manufacturing costs. It is also desirable that the manufacturing method provides a torque tube having an elongated tube with at least the same temper of current elongated tubes.

SUMMARY OF THE INVENTION

[0011] The present invention provides a torque tube and a method of manufacturing the torque tube. A method of forming a torque tube is provided. The method includes forming a fitting having an elongated tube conforming area. The conforming area includes chamfer areas having upper surfaces, lower surfaces, and chamfer surfaces that transition between the upper surfaces and the lower surfaces and has chamfer angles of approximately 20 relative to the lower surfaces. An elongated tube is procured and an end portion of the elongated tube is formed onto the conforming area to form a torque-transmitting coupling. The torque tube is also provided and formed according to the above-stated method.

[0012] The present invention has several advantages over existing torque tube manufacturing methods. One advantage of the present invention is that it provides a torque tube with increased strength and less susceptibility to cracking in a chamfer area, thus providing a torque tube with increased fatigue life.

[0013] Another advantage of the present invention is that it provides a manufacturing method that contains a decreased amount of manufacturing steps by eliminating a need for heat treating, subsequent chilling of, hand straightening of, and minimizing natural aging time of the elongated tube. The present invention by reducing the amount of manufacturing steps not only decreases production cycle time and manufacturing costs but also eliminates disadvantages associated with the eliminated steps.

[0014] The present invention itself, together with further objects and attendant advantages, will be best understood by reference to the following detailed description, taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a perspective view of an end fitting of a traditional torque tube;

[0016]FIG. 2 is a cross-sectional close-up view of chamfer areas and groove areas of a traditional torque tube;

[0017]FIG. 3 is a logic flow diagram illustrating a conventional “W” forming torque tube manufacturing process;

[0018]FIG. 4 is a perspective view of a trailing edge flap control system for an aircraft having a torque tube in accordance with an embodiment of the present invention;

[0019]FIG. 5 is a perspective view of a fitting of the torque tube of FIG. 4 in accordance with an embodiment of the present invention;

[0020]FIG. 6 is a cross-sectional close-up view of a chamfer area of the torque tube of FIG. 4 in accordance with an embodiment of the present invention;

[0021]FIG. 7 is a logic flow diagram illustrating a method of manufacturing the torque tube of FIG. 4 in accordance with an embodiment of the present invention; and

[0022]FIG. 8 is a plot of reduction in tube wall thickness versus fitting chamfer angle in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0023] Referring now to prior art FIGS. 1 and 2, a perspective view of an end fitting 10 and a cross-sectional close-up view of chamfer areas 12 and groove areas 13 of a traditional torque tube 14 are shown. The torque tube 14 has an elongated cylindrical tube 16 having a tube wall 17 and a longitudinal axis 18 extending through a center of and along length of the tube 16. An end 20 of the elongated tube 16 is coaxially formed and fixed onto the fitting 10. Only one end 20 of the elongated tube 16 is shown, typically, a second end of the elongated tube is formed and fixed to a second fitting, similar to fitting 10.

[0024] The fitting 10 has multiple chamfered surfaces 22, between a pair of upper flat surfaces 24 and multiple lower flat surfaces 26, with chamfer angles 28 that are approximately 45 relative to the lower surfaces 26. The upper surfaces 24 transition to the chamfer surfaces 22 at a relatively sharp chamfer edges 30. The chamfer edges 30 correspond with upper notches 32 that is formed in a chamfer portion 34 of the elongated tube 16 that is formed over the chamfer edges 30.

[0025] The fitting 10 also has multiple overflow groves 35 that transition between recessed areas 36 and the lower flat surfaces 26. Lower notches 37, similar to upper notches 32 are formed in groove portions 38 of the elongated tube 16 over groove edges 39.

[0026] Thinning occurs in the chamfer portion 34 and the groove portion 38 near the notches 32 and 37 as shown and can cause fatigue cracking over time as indicated by reference number 36. Thinning occurs due to a combination of compression stress with additional bending against chamfer edge 30 and groove edge 39, which causes high stress concentrations in the portions 34 and 38, respectively, reducing fatigue life. Cracking, as known in the art, reduces fatigue life of a component and is therefore undesirable. Thinning occurs due to bending and stretching experienced by the elongated tube 16 during forming of the tube 16 onto the fitting 10 during manufacturing of the torque tube 14, which is described in more detail below.

[0027] Referring now to prior art FIG. 3, a logic flow diagram illustrating a conventional “W” forming torque tube manufacturing process is shown. Elongated tubes are normally procured having a T-3 temper condition and are of various sizes, as generally indicated by step 40. The elongated tubes are treated with a chemical film such as alodine to create a corrosive inhibiting surface coating, as generally indicated by step 42.

[0028] In step 44, the elongated tubes are heat treated for an extended period of time in a furnace such that the elongated tubes are of a solid solution or in a W tempered condition. Aluminum material of the elongated tubes when in the W condition is of a lower strength temper than that of aluminum material in the T-3 condition. The elongated tubes are more malleable in the W condition than when in the T-3 condition, allowing the tubes to be formed over edges to a greater degree with less forming stress. A disadvantage with heat treating the elongated tubes, is that the corrosive inhibiting surface coating is negatively affected during the heat treatment.

[0029] In step 46, the elongated tubes are placed in a freezer to maintain the W condition and prevent aging of the tubes up until forming of the tubes.

[0030] In step 48, the elongated tubes are formed over the end fittings. The portions of the end fittings are inserted into ends of the elongated tube and then electromagnetically formed over the inserted portions of the fittings to conform the tube onto the end fittings. Electromagnetic forming is used since it is an efficient, high volume, precisely repeatable production process. During electromagnetic forming the ends of the elongated tubes are compressed via an electromagnetic pulse or impact from a magnetic coil. Chamfer portions of the elongated tubes are under tension and stretched over the sharp chamfer edges in the fittings forming the notches. During forming of the elongated tubes, thickness of the tube walls is significantly thinned in the chamfer portions. Due to the stretching of the material and thinning of the walls in the chamfer portions, the tubes are weakened and are susceptible to cracking under fatigue therein. Thinning can be difficult to detect by ordinary inspection procedures without destructive testing.

[0031] In step 50, depending upon length of an elongated tube, the elongated tube is hand straightened. During heat treatment the elongated tubes that are longer in length tend to warp or disfigure such that straightening is required before use.

[0032] In step 52, the elongated tubes are naturally aged to a T-42 temper until a significant amount of tubes are ready for artificial aging, due to costs of operating a furnace as to perform artificial aging.

[0033] In step 54, the elongated tubes are artificially aged in a furnace to again alter temper of the tubes from having a T-42 temper to having a T-62 temper, which is of a strength suitable for application use.

[0034] The above-mentioned process of manufacturing a torque tube is time consuming and costly due the amount of steps within the process and the requirements for each step.

[0035] In each of the following figures, the same reference numerals are used to refer to the same components. While the present invention is described with respect to a torque tube of an aircraft and a method of manufacturing the torque tube, the present invention may be adapted for various applications including ground-based vehicles, aeronautical vehicles, watercraft, fuselage torque tubes, door torque tubes, landing systems, and other applications known in the art that require the use of torque tubes.

[0036] In the following description, various operating parameters and components are described for one constructed embodiment. These specific parameters and components are included as examples and are not meant to be limiting.

[0037] Referring now to FIG. 4, a perspective view of a trailing edge flap control system 60 for an aircraft 62 having a torque tube 64 in accordance with an embodiment of the present invention is shown. The system 60 includes a power drive unit 66 that is mechanically coupled to and rotates the torque tube 64 via multiple angled gearboxes 70. The torque tube 64 is mechanically coupled to multiple flap transmissions 72, which transfer rotational energy from the torque tube 64 to multiple ball screws and gimbals 74 that translate a flap 76. The above-described system is an example of an application for the torque tube 64 of the present invention; the torque tube 64 may be applied in various other applications as indicated above. Also, the torque tube 64 may be of various size, shape, type, and style as known in the art.

[0038] Referring now to FIGS. 5 and 6, a perspective view of a fitting 80 and a cross-sectional close-up view of chamfer areas 82 of the torque tube 64 in accordance with an embodiment of the present invention are shown. The torque tube 64 includes one or more torque transmitting couplings 84. Each torque-transmitting coupling has an elongated tube 86 that is formed onto at least one fitting, such as fitting 80.

[0039] The fitting 80 includes an elongated tube conforming area 88 having a pair of upper surfaces 90 and lower surfaces 92, therebetween. The chamfer surfaces 94 and the lower surfaces 92 transition to overflow groove areas 93 over groove edges 95. Chamfer surfaces 94 provide transition between the upper surfaces 90 and the lower surfaces 92. Each upper surface 90 separately and in combination with, the lower surfaces 92, and a corresponding chamfer surface 94 forms the chamfer areas 82. The chamfer surfaces 94 are at chamfer angles 96 of approximately 20 relative to the lower surface 92. Note that the fittings of the present invention do not include a lower flat portion as that of the prior art, due to the chamfer angles 96. Chamfer arced surfaces 98 exists between the chamfer surfaces 94 and the upper surfaces 90, having a significantly sized radius 100 that provides a smooth transition therebetween. The fitting 80, although being preferably formed of stainless steel so as to withstand forming of the elongated tube onto the fittings without deformation, may be formed of other materials known in the art.

[0040] The elongated tube 86 has a tube wall 102 that is cylindrically shaped having a thickness 103 that may be a single continuous thickness or may be a varying thickness along a centerline 104 of the tube 86. The tube wall 102 has chamfer portions 105 that correspond to chamfer areas 82. The elongated tube 86 is preferably formed from 2024 aluminum for inherent lightweight and strength characteristics of the aluminum. Of course, other materials known in the art may be utilized including, steel, copper, brass, or a nickel alloy.

[0041] Referring now also to FIG. 7, a logic flow diagram illustrating a method of manufacturing a torque tube in accordance with an embodiment of the present invention is shown.

[0042] In step 110, the fitting 80 is formed as described above to have the chamfer angles 96 of approximately 20 and the chamfer arced surfaces 98 having radii 100 between the chamfer surfaces 94 and the upper surfaces 90. The chamfer angles of approximately 20 and the chamfer arced surfaces 98 minimize thinning and stressing of the elongated tube 86 during forming of the tube 86 onto the fitting 80, which is described in more detail below.

[0043] In step 112, the elongated tube 86 is procured having preferably a T-3 temper for the application of FIG. 4. Industry standard processes are utilized to extrude, handle, draw, and treat the elongated tube 86. The elongated tube 86 is formed such that there is no seam in the tube wall 102.

[0044] In step 114, the elongated tube 86 is corrosive inhibit treated by applying a chemical coating or first layer such as alodine to the tube walls 102 to form a first corrosive inhibiting layer 107, using methods known in the art. A second corrosive inhibiting layer 108 may also be applied, such as paint or other similar material known in the art, to further aid in prevention of corrosion. In one embodiment of the present invention the second layer is applied to an interior surface 109 of the tube walls 102.

[0045] In step 116, an end portion 106 of the elongated tube 86 is formed onto the elongate tube conforming area 88 to form a torque-transmitting coupling 84. The elongated tube 86 is formed onto the fitting 80 without creating notches in the tube wall 102, unlike that of prior art torque tube manufacturing methods. Although, it is preferred that the elongated tube 86 be electromagnetically formed onto the fitting 80, other forming techniques may be used to exert pressure on the tube wall 102 to deform it around the fitting 80 including swaging, hydroforming, rubber press forming, or explosive forming. Amount of stretching and stress experienced, during forming of the tube 86, is minimized due to the fitting 80 having the chamfer angles 96 of approximately 20 and the chamfer arced surfaces 98, thereby also minimizing amount of thinning of the tube wall 102 over the chamfer areas 82. In one embodiment of the present invention, upon completion of forming the elongated tube 86 onto the fitting 80 the thickness 103 of the tube wall 102 over the chamfer arced surfaces 98 is approximately 0.0795 inches as compared to that of the prior art, which is approximately 0.0716 inches thick over the chamfer edges, thus a significant minimization in thinning from an original tube wall thickness of 0.0831 inches exists utilizing the present invention. This difference in thickness of the tube wall 102 significantly improves fatigue life in the chamfer portions 105.

[0046] In step 118, the elongated tube 86 is artificially aged in a furnace for a period of time, as known in the art. Upon completion of artificial aging, the aluminum material of the tube wall 102 is of a T-81 temper, which has approximately equivalent mechanical properties to that of aluminum having a T-62 temper as elongated tubes of the prior art. Thus, the present invention eliminates the need to naturally age the elongated tube whereby aluminum material in a W condition is converted to have a T-42 temper, which can then be converted to have a T-62 temper by artificial aging. The present invention, through artificial aging, directly converts the elongated tube 86 having a T-3 temper to having a T-82 temper.

[0047] Referring now to FIG. 8, a plot of reduction in tube wall thickness versus fitting chamfer angle in accordance with an embodiment of the present invention is shown. The thickness 103 in the chamfer portions 105 is generally thinned during forming of the elongated tube 86 onto the fitting 80, due to stretching of the tube wall 102. As chamfer angles 96 are decreased, the amount of thinning of the tube wall 102 is decreased, as illustrated by curve 120. Unfortunately, ability to decrease the chamfer angles 96 is limited by strength of the coupling 84 between the elongated tube 86 and the fitting 80. The smaller the chamfer angles 96 the less force is needed to axially pull out the fitting 80 from the elongated tube 86. Also, for every smaller increment in chamfer angles 96 there is smaller difference in thickness of the formed tube wall 102. For example, when the chamfer angles 96 are decreased from 45 to 40, the difference in thickness 103 is approximately 2%, unlike when the chamfer angles 96 are decreased from 25 to 20, the difference in thickness 103 is approximately 0.8%.

[0048] As known in the art, it is desired that the torque-transmitting coupling 84 be stronger than that of the elongated tube 86 itself and be able to withstand fatigue loading for a period exceeding approximately four times a service life of the aircraft 62. The greater strength of the torque-transmitting coupling 84 over that of the elongated tube 86 better assures that a failure in the coupling 84 does not occur during loading. Thus, in order to have a torque transmitting coupling 84 that has the desired strength and is formed so as to minimize cracking in the chamfer portions 105, chamfer angles 96 of approximately 20 are utilized.

[0049] The above-described steps are meant to be an illustrative example, the steps may be performed synchronously, continuously, or in a different order depending upon the application.

[0050] The present invention provides a torque tube manufacturing method that eliminates forming of chamfer and groove notches within an elongated tube of a torque tube as formed in prior torque tube manufacturing methods. The present invention also forms a torque tube with a minimum amount of thinning and stress in chamfer portions during forming of elongated tubes onto fittings and during loading of the elongated tubes. By minimizing crack initiation and growth within tube walls, fatigue life is increased. The present invention also eliminates the need for heat treatment and chilling of the T-3 tempered elongated tubes before forming, which reduces manufacturing time between procurement of the elongated tubes to forming of the elongated tubes by approximately 50%. The present invention by eliminating a need for several manufacturing steps reduces amount of production equipment needed to produce a torque tube. Thus, the present invention reduces costs involved in the manufacturing of torque tubes.

[0051] The above-described apparatus and method, to one skilled in the art, is capable of being adapted for various applications and systems known in the art. The above-described invention can also be varied without deviating from the true scope of the invention. 

What is claimed is:
 1. A method of forming torque transmitting coupling comprising: forming at least one fitting having an elongated tube conforming area comprising forming at least one chamfer area having an upper surface, a lower surface, and a chamfer surface that transitions between said upper surface and said lower surface and has a chamfer angle of approximately 20 relative to said lower surface; procuring an elongated tube; and forming an end portion of said elongated tube onto said elongated tube conforming area to form the torque-transmitting coupling.
 2. A method as in claim 1 wherein forming at least one fitting comprises forming an arced surface between said chamfer surface and said upper surface that has a significantly sized radius.
 3. A method as in claim 1 further comprising corrosive inhibit treating said elongated tube.
 4. A method as in claim 2 wherein corrosive inhibit treating said elongated tube comprising applying an alodine film to said elongated tube.
 5. A method as in claim 1 wherein forming an end portion of said elongated tube comprises electromagnetically forming said end portion of said elongated tube onto said elongated tube conforming area.
 6. A method as in claim 1 further comprising aging said elongated tube.
 7. A method of forming a torque tube comprising: forming at least one fitting having an elongated tube fusing area comprising forming at least one chamfer area having an upper surface, a lower surface, and a chamfer surface that transitions between said upper surface and said lower surface and has a chamfer angle of approximately 20 relative to said lower surface; procuring an elongated tube; and forming an end portion of said elongated tube onto said elongated tube conforming area to form a torque-transmitting coupling.
 8. A method as in claim 7 further comprising corrosive inhibit treating said elongated tube.
 9. A method as in claim 8 wherein corrosive inhibit treating said elongated tube comprising applying an alodine film to said elongated tube.
 10. A method as in claim 7 wherein forming an end portion of said elongated tube comprises electromagnetically forming said end portion of said elongated tube over said at least one fitting.
 11. A method as in claim 7 further comprising artificially aging said elongated tube.
 12. A method as in claim 7 wherein aging said elongated tube is performed artificially.
 13. A method as in claim 7 wherein forming at least one fitting comprises forming an arced surface between said chamfer surface and said upper surface that has a significantly sized radius.
 14. A torque tube formed according to the method of claim
 7. 15. A torque tube comprising: at least one fitting having an elongated tube fusing area comprising: at least one upper surface; at least one lower surface; and at least one chamfer surface forming at least one chamfer area with said at least one upper surface and said at least one lower surface and having a chamfer angle of approximately 20 relative to said at least one lower surface; and an elongated tube having at least one end portion formed onto said elongated tube fusing area.
 16. A torque tube as in claim 15 further comprising an arced surface between said at least one chamfer surface and said at least one upper surface that has a significantly sized radius.
 17. A torque tube as in claim 15 wherein said at least one end portion of said elongated tube is electromagnetically formed onto said at least one fitting.
 18. A torque tube as in claim 15 wherein said elongated tube has at least one corrosive inhibiting layer.
 19. A torque tube as in claim 18 wherein said at least one corrosive inhibiting layer comprises an alodine layer and a paint layer.
 20. A torque tube as in claim 15 wherein said elongated tube is aged to have a T-81 temper. 